The present invention relates to light detectors and more particularly to a light detector having an ultrafast gated input.
There is a need for a light detector having an input that can be gated on and off over an ultrashort time window, such as in picoseconds. For example, it is well known that Raman scattering signals produced when a sample is excited by a light source respond instantaneously following the shape of the impinging light signal, which may be a pulse on the order of picoseconds, while the fluorescence emission times are generally greater than a few nanoseconds. In order to measure the intensity of the Raman signals it would therefore be desirable to provide a light detector that can be gated on and off for a time period that is not longer than the excitation pulse.
Photomultiplier tubes are well known in the art and commonly used as light detectors to measure the intensity of light inpinging thereon. These tubes generally include a photocathode which receives a light signal and produces emission of electrons in proportion to the intensity of the impinging light and some form of electron multiplication means, such as a dynode chain for amplifying the emitted electrons.
Streak cameras are short about ten years old in the art and have been used, hitherto, to directly measure the time dynamics of luminous events, that is to time resolve a light signal. A typical streak camera includes an entrance slit which is usually rectangular, a streak camera tube, input relay optics for imaging the entrance slit onto the streak camera tube, appropriate sweep generating electronics and output-relay optics for imaging the streak image formed at the output end of the streak camera tube onto an external focal plane. The image at the external focal plane is then either photographed by a conventional still camera or a television camera. The streak camera tube generally includes a photocathode screen, an accelerating mesh, sweeping electrodes and an phosphor screen. The streak camera tube may also include a microchannel plate. Light incident on the entrance of the streak camera is converted into a streak image which is formed on the phosphor screen with the intensity of the streak image from the start of the streak to the end of the streak corresponding to the intensity of the light incident thereon during the time window of the streak. The time during which the electrons are swept to form the streak image is controlled by a sweep generator which supplies a very fast sweep signal to the sweeping electrodes. The input optics of the streak camera, in the past, has been a single lens.
In an article entitled "An Ultrafast Streak Camera System" by N. H. Schiller, Y. Tsuchiya, E. Inuzuka, Y. Suzuki, K. Kinoshita, K. Kamiya, H. Iida and R. Alfano appearing in the June, 1980, Edition of Optical Sprectra, various known streak camera systems are discussed. The article is incorporated herein by reference.
In U.S. Pat. No. 4,232,333 to T. Hiruma et al there is disclosed a streak image analyzing device in which the output streak image of a streak camera is fed into a television camera. The output of the television camera is fed through a videomixing circuit to a monitor. The output of the television camera is also fed to an integrating circuit through a gate circuit. The output of the integrating circuit is fed to a memory through an analog to digital converter. The output of the memory is displayed by a display unit and/or fed back into the videomixing circuit.
In an article entitled Picosecond Characteristics Of A Spectrograph Measured By A Streak Camera/Video Readout System by N. H. Schiller and R. R. Alfano appearing in the December 1980, issue of Optical Communications, Volume 35, No. 3. pp. 451-454, a streak camera/video readout system is disclosed.
Another article pertaining to streak cameras and spectrographs is Coupling An Ultraviolet Spectrograph To A Scloma For three Dimensional Picosecond Flurorescent Measurements by C. W. Robinson et al in Multichannel Image Detectors pp. 199-213 ACS Symposium Series 102, Amercian Chemical Society.
Known patents of interest include U.S. Pat. No. 2,823,577 to R. C. Machler; U.S. Pat. No. 3,385,160 to J. B. Dawson et al; U.S. Pat. No. 2,436,104 to A. W. Fisher et al; U. S. Pat. No. 3,765,769 to E. B. Treacy; U. S. Pat. No. 4,060,327 to Jacobowitz et al; U. S. Pat. No. 4,162,851 to A. Wade; U. S. Pat. No. 4,299,488 to W. J. Tomlinson and U.S. Pat. No. 4,320,971 to N. Hashimato et al.
It is the general purpose of this invention to provide a light detector having an ultrafast input gate.
Accordingly, it is an object of this invention to provide a new and improved light detector.
It is another object of this invention to provide a light detector having an input that can be gated on and off.
It is still another object of this invention to provide a light detector having an input that can be gated on and off in picoseconds.
It is yet still another object of this invention to provide a light detector which utilizes sweeping electronic such as found in a streak camera as a mechanism for gating on and off a light detector.
The foregoing and other objects and advantages will appear from the description to follow. In the description, reference is made to the accompanying drawing which forms a part thereof, and in which is shown by way of illustration, a specific embodiment for practicing the invention. This embodiment will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims.